What is lighting my scene?
The only other "light" source in blender is the Ambient Occlusion. Its not real light but purely a rendering trick that tends to look nice because generally in real-world surfaces that are close together (like small cracks) will be darker than surfaces that do not have anything in front of them, because of shadows, dirt, etc.

You can disable it in the World Properties under the tab Ambient Occlusion.